The present invention relates to an electrical connector between relatively rotating elements. More specifically, the present invention is a rolling electrical transfer to improved transfer coupling members between the rotating and the stationary components.
The present invention relates to an electrical connector between relatively rotating elements. Electrical equipment such as radar and ship antennas have a need to transmit power and data between stationary equipment and relatively rotating equipment. Electrical connectors that can accommodate constant rotation are needed for these types of applications. Many such electrical connectors exist, but with a variety of deficiencies.
Slip rings have a long history of applications for the transfer of electrical signals and power across a rotating interface. The sliding action between the brush and the ring results in significant drag torque and wear debris. Although a number of improvement patents have been granted for slip rings sets which have improved brush designs such as bundles of conductive fibers, additional improvements are still required. These include an elimination of trades of such parameters as brush pressure and contact area on electrical noise resistance, wear, life, and torque, and sensitivities of brush and ring material on air, fluid and vacuum environments. Maintainability costs related to brush seizure and failure are also excessive.
Rolling electrical conductor assemblies offer performance and life improvements. These concepts, however, are not broadly new and have heretofore been proposed for use in place of the more conventional slip ring and brush assemblies. Early rolling types of conductor assemblies exist, such as those disclosed in U.S. Pat. Nos. 2,467,758 and 3,259,727. U.S. Pat. No. 3,259,727 describes a coil spring coupler design to electrically connect the stationary and the rotary components of the transfer device. This multi-turn spring configuration is more economical to fabricate than a single hoop but imposes increased stress levels for a given preload. A rolling electrical conductor assembly that achieves an economical fabrication benefit without imposing greater stress is needed.
Important improvements have since been developed as disclosed by U.S. Pat. Nos. 4,068,909; 4,098,546; 4,141,139; 4,335,927; 4,372,633 and 4,650,226 which disclose rolling electrical interface configurations for both low level signals and for power. These configurations all use band shaped cylindrical flexible couplers, which are captured in concave grooves in two concentric tracks to electrically connect the rings. The couplers have compliance so as to be preloaded between the two rings. These second-generation transfer configurations provide longer life and near absence of alignment and preload sensitivities, wear debris and rotational torque and greater transfer current capacity. They tend to be relatively expensive to design and manufacture, however, without restricting the potential performance and life benefits. Additional improvements are still required, therefore, to meet the ever-increasing demands of the industry. New improvements are required in rolling electrical transfer components to provide reliable operation for hundreds of millions of bi-directional revolutions without producing significant wear debris, to transfer higher steady-state and surge currents, to eliminate electrical transfer sensitivities to externally induced contaminants and to reduce manufacturing costs.
U.S. Pat. Nos. 5,009,604 and 5,429,508 describe coupler designs for transferring electrical signals between stationary sensors and rotatable steering wheel mounted components such as air bags. One of these coupler designs, which electrically couples the stationary and rotatable component, is of a hoop shape and is rolled out of sheet stock with an over-lapping region. Another uses resilient spheres, which roll in grooved tracks in the stationary and rotational components. The hoop configuration is cost effective and allows thicker material to be used which is advantageous, but tests in grooved tracks have demonstrated a speed limit of only a few hundred RPM because of mechanical discontinuity at the over-lap region. The speed limit is lower in the rotation direction, which causes the over-lap section to advance into the contact interfaces. Debris is generated as the ends of the over-lapped region bi-directionally slide against one another while the radial load moves around the rolling coupler, which reduces its operational life. Examination of couplers after test has identified the source of the speed limit, wear and debris as variations of roundness at the contact diameter and associated preload perturbations during operation. The spherical couplers require multiple components per track, which necessitates the addition of a guide plate assembly, and associated sliding induced component wear.
In all of the listed patents and prior art, the coupler, is predominantly a flexible member, which rides in, and is captured in, the curved tracks in the two conductive members. For those cases where the coupler is not flexible, the fixed and/or rotating members provide the necessary compliance since the coupler is radially preloaded in the tracks. In all of the cited configurations the member-to-member radial annulus space and the radial variations in the track-to-track spacing are accommodated by the radial compliance of the coupler. This rolling deflection results in stress cycling of the coupler as the member and coupler rotates. The configuration is such as to result in more coupler cycles than member rotations. The effect of stress cycling on coupler fatigue life must be carefully considered for each design which must factor in the fatigue characteristics of the coupler material. This requires a knowledge of the material heat treat and process work hardening effects. This information is usually not available at the design stage of the coupler and must be determined by experience.
The roll ring configuration of U.S. Pat. No. 4,372,633 provides increased current transfer capacity by way of increased numbers of couplers, which couple the members. This configuration also uses idlers between the couplers to avoid rubbing friction and wear between adjacent couplers. This configuration also provides guide rails mounted to the inner member to assure that all of the track and coupler interfaces are in rolling contact. The band shaped coupler configuration is costly to fabricate, inspect and plate. Coupler designs that provide the necessary compliance for fitting and preloading between the tracks are thin-walled, hence limiting the transfer current per coupler and the contact areas with the tracks. The contact interfaces exhibit low wear because of the rolling action and the low preload required. Unfortunately, the parameters that lead to low wear also exhibit greater sensitivity to contaminants at the interfaces, which can result in a variation of electrical transfer resistance. This problem specifically affects operations in severe contamination environments such as encountered for helicopter mastheads and tank turrets. The simultaneous requirements of appropriate assembled deflection, current density, contact preload and fatigue life complicates and compromises the design process and results in a flexure wall which is usually thin, on the order of 0.1 mm or so. Additionally, since the coupler walls are thin, it is often not possible to provide proper edge profiles. The operational life and performance is related to this profile. Therefore, it is important to reducing interface sliding and current density to acceptable levels. The thin wall coupler is also difficult and costly to fabricate because of its compliance.
The application of this multi-coupler transfer design is also size limited since the configuration requires that the annulus space between the two concentric rings be filled with a full complement of couplers and idlers. This design is not cost effective because it contains non-utilized current capacity. Improved coupler design configurations are required which have reduced fabrication costs and allow the use of an optimum number of couplers.
U.S. Pat. No. 5,501,604 describes a multi-coupler electro-mechanical transfer unit design which uses a set of planetary gears to couple a set of planetary rolling preloaded couplers with the rings. In this configuration, the contact rings are coupled to the sun and ring gears of the planetary set. This configuration has the advantage of allowing the use of a greater number of couplers to satisfy a greater transfer current requirement without requiring the use of a full complement. The addition of gearing, however, increases the fabrication cost and decreases the life because of gear wear and the complexity of trying to use a lubricant for the gearing without contaminating the electrical interfaces. In addition, since the couplers ride on a thin compliant tubular carrier which is common to the planet gears, the allowable deflections and misalignments are not as great as that of the early configurations of multi-flexure arrangements such as described in U.S. Pat. Nos. 4,068,909 and 4,372,633.
The aforementioned difficulties with respect to the transfer of electrical energy between relatively rotatable members are to a great extent alleviated through the practice of the present invention. The present invention provides an electrical conductor assembly having a pair of coaxial conductive members relatively rotatable about a common axis coupled together by pairs of coupler halves, the profile edges of which make contact with matable tracks on the conductive members. Unlike the prior art electrical conductor assemblies which have a flexible coupler preloaded in the track space, the present invention accomplishes the same efficient rolling transfer but without imposing material fatigue design constraints. Additionally, the invention accommodates the use of a selected number of pairs of coupler halves making possible the transfer of increased electrical current by means of a greater number of parallel paths. Unlike the prior art, the inventive coupler halves may be fabricated out of electrically conductive metal sheet stock, which provides enlarged opportunities for optimum material selection. Coupler half-track designs are made possible by the present invention to allow for a variety of contact preloading means and track configurations on the conductive members.